Project summary/abstract Sarcoidosis, a multisystem granulomatous disorder of yet unknown etiology, is characterized by formation of noncaseating granulomas. The granulomas almost always occur in lungs, but other organs, including skin, eye and heart, can be affected as well. The granulomatous inflammation causes organ dysfunction and ultimately fibrosis which are associated with morbidity and mortality. In the United States, the sarcoidosis annual adjusted incidence rate in Caucasians is about 11 in 100,000 and 34 in 100,000 in African Americans. Hypergammaglobulinemia, autoantibody production and circulating immune complexes are frequently associated with sarcoidosis, indicating that humoral immunity, and B cells in particular, may be involved in pathogenesis of this disease. Supporting this hypothesis several recent studies suggest abnormal B cells responses in sarcoidosis patients. We recently described a population of T-bet+/CD11c+ B cells (previously named ABCs), which appear in autoimmune prone mice and humans. A combination of TLR7, IFN?R and BCR signaling leads to a high level of T-bet expression in B cells. This in turn leads to B cell differentiation into CD11c+ B cells and IgG2a/c isotype class-switch (in mice). Interestingly, the same factors (IFN? and TLR7) have been reported to play a role in sarcoidosis. These data led us to the hypothesis that T-bet+/CD11c+ B cells might be present in sarcoidosis patients and might be involved in the pathology of this disease. The data obtained from murine T- bet expressing B cell indicate that this B cell subset is enriched in autoreactive B cells, can produce high titers of autoantibodies, and is more efficient in antigen processing and presentation than other B cells. Thus we suggest that high levels of IFN? and involvement of TLR7 can lead to the appearance of T-bet+/CD11c+ B cells in sarcoidosis patients. This B cell subset might affect the development of the disease by production of autoantibodies and/or by antigen presentation to T cells. We will pursue the following Aims: Aim 1. To assess the frequency of T-bet+/CD11c+ B cells in sarcoidosis patients, their presence in granulomas and its correlation with clinical data. Aim 2. To explore the properties of T-bet+/CD11c+ B cells in sarcoidosis patients Aim 3. To determine the function of T-bet+/CD11c+ B cells in sarcoidosis patients The unique accessibility to the sarcoidosis and IPF disease controls samples at National Jewish Health (NJH serves as a local and national referral center for sarcoidosis) creates a great opportunity for studying this disease (especially, since there is no animal model). The sarcoidosis biorepository has recruited over 800 patients to date and continues to recruit sarcoidosis patients. In addition the combination of Dr. Hamzeh?s expertise in sarcoidosis and Dr. Rubtsova?s expertise in B cells biology creates a uniquely strong foundation for a successful accomplishment of this proposal.